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New Design Feed Channel Spacer in Spiral Wound Elements for Pretreatment Cost Reduction

Desalination Systems, Inc.; Escondido CA.
September 1998

Report #45 - Abstract -

The objective of this work was to examine whether a new type of feed channel spacer, called a parallel spacer, in spiral wound elements would decrease the pretreatment requirement, when operating RO/NF elements on municipal wastewater. The new design feed channel spacer consisted of thicker longitudinal strands, which define the spacer thickness, and thinner cross strands (perpendicular to the thicker strands), which were not in contact with the membrane surface.

RO/NF elements with the parallel spacer and the standard diamond shape spacer operated on tertiary treated municipal wastewater for six months. The elements with the standard diamond shape spacer performed better than the elements with the parallel spacer. A nominal 5um melt blown cartridge filter stopped the particulate material which otherwise would have increased the pressure drop over the elements, but did not stop colloidal material which caused a rapid decline in water permeability of the elements. Alkaline cleaning removed brown deposits, but did not remove a thin transparent slimy layer from the membrane surface. This slimy layer was probably the cause of the rapid decline in membrane performance after cleaning. If this slimy layer can be prevented from forming, or if it can be removed by cleaning, the permeate flux of RO/NF elements, without MF as pretreatment, can most likely be maintained at 101/m2/hr (6 gfd) and possibly 151/m2/hr (9 gfd).


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